Today Oracle released its latest version of Solaris technology, the Oracle Solaris 11 Express 2010.11 release. It includes a large number of new features not found in either Oracle Solaris 10 or previous OpenSolaris releases including ZFS encryption and deduplication, network-based packaging and provisioning systems, network virtualization, optimized I/O for NUMA platforms and optimized platform support including support for Intel's latest Nehalem and SPARC T3. In addition, Oracle Solaris 10 support is available from within a container/zone so migration of existing systems is greatly simplified. The release is available under a variety of licenses including a supported commercial license on a wide variety of x86 and SPARC platforms.

The point being if only Solaris is supporting ZFS (and taking into account Oracle doesn't favour open source like Sun did), then ZFS might quickly become obscure tech only available to Oracle licensees.

As BtrFS is GPL, I could see many people favouring BtrFS for the long game than an increasingly closed ZFS for the short game. In fact we already see this with Linux (though Linuxes situation differs slightly due to license incomparability so improving BtrFS might prove quicker than reverse engineering ZFS for the sake of having GPL code), but thankfully I'm not loyal to Linux like many of my fellow open source advocates are. But lets face it, as much as I like Unix, Linux does have massive clout these days so there is already a massive demand for BtrFS.

So if 5 years down the line, the majority of the industry outside of Oracle are favouring BtrFS, then why would Oracle care about ZFS internally? Particularly when I'm yet to see any evidence that they're migrating their own databases from Redhat to Solaris (or at least they're not on any of the servers my organisation leases from them)

There has been plenty of occasions where the more mature of two technologies have fallen out of favour. So I wouldn't say ZFS was sitting comfortably just because it has a few years on it's rivals. If anything, I would say it's fucture was uncertain because FreeBSD is the only non-Oracle OS that seems to properly support that file system.